The Hubble Space Telescope's image of the Crescent Nebula revealed that the shell of matter surrounding the aging star HD 192163, is a network of filaments and dense knots, all enshrouded in a thin "skin" of gas [seen above in blue]. The skin is glowing because it is being blasted by ultraviolet light from HD 192163.
Hubble's view covers a small region at the northeast tip of the structure, which is roughly three light-years across. A picture taken by a ground-based telescope [lower right] shows almost the entire nebula. The whole structure is about 16 light-years wide and 25 light-years long. The bright dot near the center of NGC 6888 is HD 192163. The white outline in the upper left-hand corner represents Hubble's view.
After only 4.5 million years (one-thousandth the age of the Sun), HD 192163 began its headlong rush toward a supernova catastrophe. First it expanded enormously to become a red giant and ejected its outer layers at about 20,000 miles per hour. Two hundred thousand years later - a blink of the eye in the life of a normal star - the intense radiation from the exposed hot, inner layer of the star began pushing gas away at speeds in excess of 3 million miles per hour!
When this high speed "stellar wind" rammed into the slower red giant wind, a dense shell was formed. In the image, a portion of the shell is shown in red. The force of the collision created two shock waves: one that moved outward from the dense shell to create the green filamentary structure, and one that moved inward to produce a bubble of million degree Celsius X-ray emitting gas (blue). The brightest X-ray emission is near the densest part of the compressed shell of gas, indicating that the hot gas is evaporating matter from the shell. The massive star HD 192183 that has produced the nebula appears as the bright dot at the center of the full-field image.
HD 192163 will likely explode as a supernova in about a hundred thousand years. This image enables astronomers to determine the mass, energy, and composition of the gaseous shell around this pre-supernova star. An understanding of such environments provides important data for interpreting observations of supernovas and their remnants.
Provided by The Daily Galaxy - NASA/Chandra Xray Space Telescope
